help:crystal oscillator circuit

hi..i hv a problem designing a crystal oscillator circuit..it looks like the gate circuit in figure below but without the NAND gate..the crystal have a frequency of 8Mhz..how do i get the value of the resistors?



thanx in advance..

 

Ahhh - the gate circuit without the NAND gate?

What are you using instead to excite the crystal?

 

the gate circuit doesn't have any transistors..and in the circuit i want to use,it is similar to the circuit written "Gate" in the figure but it doesnt hv the NAND gate..how the crystal is excited im not sure since it is connected to the CLK pin of a chip..i guess the best way for me to get the value of the resistors is by doing the good old try n error..i hope i'll find a value..thanx anyways..

 

Bill, you're correct about those symbols being transistors.

The schematics came from here:
http://www.ieee-uffc.org/freqcontrol/tutorials/vig3/vig3.htm
"Chapter 2, Quartz Crystal Oscillators"
then 9th page down, "Oscillator Circuit Types"

 

What is the chip that you are trying to clock? Do you have a link to a datasheet?

If the datasheet has no information in it about clocking it using an xtal, go to Texas Instrument's site and get their datasheet for a CD4045B CMOS IC.

On the first page there's a similar xtal oscillator, with suggested values given in the text on the left side of the page.

 

the circuit is connected to a Zilog Z85C30..thanx for your tips on the CD4045B ic..it was a great help..im off to test my circuit..

 

OK, I think you'll run into trouble with that circuit. You're going to need to use an inverter or two, perhaps a NAND gate, in order to get a clock signal out of that xtal.

If you use TTL level IC's, that'll change the values for the resistors.

You might try a CMOS 4093 (Quad Schmitt-trigger NAND) or 40106 (Hex Schmitt-trigger inverters). Run the unused gates/inverters in parallel to buffer the output of the xtal clock circuit.